Transmission regulation



F. A. BROOKS TRANSMISSION REGULATION Filed Oct. 8, 1935 April 6, 1937.

L F/G. 1 RI R2 ,lo I L 4 I II :1: II n, 1 (PL 1 P 2 C .2 II II M0 TORSAUTOMATIC GALVANOMETER I I AND DRIVE f n 65 H II .59 F GEAR 0 rz: g 6O=}-ro OTHER MOTORS //v VENTOR 5 6 AUTOMATIC GALVANOMETER :1: F. A.BROOKS AND DRIVE .A TTORNEV Patented Apr. 6, 1937 TES PATENTTRANSMISSION REGULATION Application October 8, 1935, Serial No. 44,047

7 Claims. (Cl. 178-44) The present invention relates to the regulationof transmission in a signaling or other system in which currents orwaves are being sent and in which the currents or waves are subject tovariations to be compensated for.

The invention will be described and illustrated as embodied in a systemfor transmitting signals in succession through a number of repeaterstations situated along a transmission line, with reg- 10 ulation at therepeater stations to compensate for variations in line characteristic.In particular, the system to be illustrated and described is a multiplexcarrier line system transmitting a Wide band of frequencies, such as 12to 60 15 kilocyc-les or 10 to 100 kilocycles in which are comprised thefrequencies utilized by a number of speech channels, for example 12 to:22, on the basis of 4 kilocycles being allotted to each channel. In thisillustrative embodiment, the

o lines are the pairs within a lead sheathed cable which may be ofordinary or known construction. The attenuation is such as to require arepeater spacing of the order of 10 to miles.

In such a system the principal transmission variable is thatcorresponding to variation in temperature of the cable, the temperaturevariations being much greater and much more rapid in the case of aerialcables than underground cable.

The variation of transmission loss with temperature is difierent atdifferent frequenciesand in a band as wide as indicated above, thedifference in transmission loss between dfierent frequences in the bandis great enough to require correction in a long system. The change inattenuation for given change in temperature is, of course, in the samedirection for all frequencies, but in cables observed by applicant it isgreatest in the range between 23 and kilocycles. The correction is madeby introducing a flat change suflicient to correct for the greatest rateof change in attenuation. This means that the flat regulator adds toomuch gain at all frequencies except the frequency or frequencies atwhich the maximum rate of change with temperature occurs. For longsystems a changing loss must be added to the cable loss at all otherfrequencies than the frequency or frequencies at which the flatregulator compensates.

This difierential or added correction is referred 5 to as the twistcorrection as distinguished from the flat correction.

In a long cable carrier system there Will ordinarily be a number ofunattended repeater stations interspersed between attended stations, for

example two to four or five unattended stations between the nearest twoattended stations.- It is desirable to keep the apparatus at theunattended stations as simple as possible and to locate as much of thecorrective mechanism as possible at the attended stations.

For this reason it is desirable to make the flat compensation at eachrepeater station While the differential or twist correction is made onlyat attended stations.

A system in general as outlined above is dis- 10 closed and claimed inH. S. Black Patent 1,956,547 granted May 1, 1934. The present inventionis concerned with various improvement features, including a novel mannerof eifecting the com pensating changes in'the repeaters both as to 15circuits and mechanisms, and various other features more or lessincidental thereto. The nature of the invention and its various objectsand features will be more clearly understood from the following detaileddescription taken in connection with the accompanying drawing in which:

Fig. 1 is a simplified schematic drawing, showing the manner ofassociation of the pilot wire lines and the controlling mechanism with aplurality of repeaters in the line; and

Fig. 2 is a schematic circuit diagram of one of the attended repeaterstations having both the short pilot line control and the long pilotline control.

In Fig. 1 it is assumed that the line It is one of several lines whichmay be included inside a lead sheath, each line equipped for multiplexcarrier telephone transmission employing frequencies in a, wide band.Every few miles along the line I0 is an unattended repeater R1, R2, etc.and at longer intervals along the line l9 are attended repeaterstations, one of which is shown at RR. A short pilot Wire such as PL1,PLz, etc., is associated with each repeater section and terminates in acontrol C1, C2, etc, for automati- 40 cally changing the gain of therepeaters R1, R2, etc., in amanner that will be described. A long pilotwire PL4 spans the entire distance between main .or attended repeaterstations such as RR and has associated with it a control mechanism 45 C4for regulating the repeater characteristic in a manner to be described.

The manner in which the control C3 regulates the gain of a. repeater atthe station RR may be the same as that used at each of the unattendedstations. The attended station, however, includes a twist compensatornetwork 9 indicated as having'its shape controlled by a connection 2 tocontrol mechanism C4. That is, the long pilot wire control mechanismoperates upon the network 9 to govern the extent of the twist correctionto compensate for the unequal change in line transmission characteristicthroughout the utilized frequency range. In order to achieve fullcorrection at the repeater station RR by the conjoint action of twocontrols C3 and C4 which exert independent control on the repeater RR,the mechanism C4 is made to control the mechanism associated with theshort pilot wire in some suitable manner as by changing a resistance l Iassociated with the short pilot wire regulating mechanism to insureproper cooperative relation between the two controlling mechanisms C3and 04.

Since as noted above the type of pilot wire control mechanism used ateach of the unattended repeater stations is the same as the pilot wirecontrol C3 at the station RR of Fig. 1, a description of the controlmechanism C3 of Fig. 2 will suffice also as a description of the controlmechanism such as C1 or G2 at unattended stations such as R1 or R2.

Referring now to Fig. 2, the line H! is shown leading inside a shieldedcompartment IT to an input transformer 1 for an amplifying repeater 8,the output transformer I3 of which couples to the succeeding section ofline in. Only so much of this figure will be considered at first asinvolves the control mechanism belonging to the short pilot wire, and ascorresponds, therefore, to the mechanism that is used at an unattendedstation. For the present, then, it will be assumed that the switches l9,19 are thrown to the left of this figure thus removing the equalizer itfrom the circuit and it will be further assumed that the repeater 20 isabsent. One other assumption is necessary, that is, that the switches 21shown associated with pilot conductor 2i (corresponding to pilot wirePL3 of Fig. 1) are thrown to their alternate positions thusdisconnecting the pilot wire conductors from the conductors 42.

Under these assumptions it will be seen that the repeater 8 is includedin the shielded box and connected between two sections of the line ill.Repeater 8 is preferably of the stabilized feed-back type disclosed andclaimed in U. S. patent application to H. S. Black Serial No. 606,871,filed April 22, 1932, in whichv a feed-back leads from the output ofrepeater 8 through an equalizer network M to the input side of repeater8 for feeding back a relatively large amount of output waves in suchmanner as to reduce the gain of the repeater circuit. The repeater 8will, in practice, comprise more than one stage of amplification andwill be designed to have the requisite high gain and suitable widetransmission band. Equalizer I4 may be a fixed equalizer network havinga transmission characteristic similar to that of a section of the lineIt for enabling the repeater circuit 8 to compensate for unequalattenuation of currents of different frequencies in the utilized band asthey are transmitted over the line H].

The feed-back circuit of the amplifier 8 is shown as including athree-plate condenser l5 and a variable condenser iii. The three-platecondenser I5 is given a fixed setting at the time the amplifier isinstalled in order to adjust the gain of the repeater to suit the lengthof the particular repeater section to which the repeater is connected.In practice, repeater sections differ in length, sometimes by severalmiles so that different amounts of gain are required at diiferentrepeaters along the line. When the gain setting has been made to theproper value by condenser IS, the condenser setting is left fixed atthat value. Variable capacity [6 is then used to control the gain of therepeater circuit as will be described. The combination of the twocondensers l5 and [6 used together in this way is specifically claimedin an application of Anderson-Mallinckrodt-Stillwell Serial No. 44,050,filed October 8, 1935. In the application of H. S. Black referred toabove, it is pointed out that if the amplification constant or [L of theamplifier 8 and the feed-back coefficient [i are so proportioned thatthe product 1.,8 is very large compared to unity, the total resultantamplification of the repeater may be made to approach the value thecoefficient B being less than unity, of course. Under thesecircumstances a variation in the capacity of condenser It can be made toproduce (in decibels) substantially linear variations in the gain of therepeater circuit as a whole and with proper circuit design the gainchange is the same throughout the utilized frequency band. In one caseused by applicant the total capacity looking toward the right from thepoint a, 0. toward the three-plate condenser l5 was 50micro-microfarads.

The mechanism for'adjusting the condenser it is controlled by the pilotwire 2! which with the switches 21 thrown to their alternate position,is connected in one arm of bridge 22 in series with fixed resistance 24.The other arms of the bridge are shown at 23, 25 and 26 with a balancingresistance 28 included between arms 24 and 26. Bridge 22 is suppliedwithcurrent from battery 3!]. An automatic galvanometer 29 is connectedacross a diagonal of the bridge, this galvanometer being preferably of atype known to the trade including a continuously rotating driving motorand a clutch mechanism under control of the galvanometer whereby whenthe bridge becomes unbalanced it is automatically rebalanced by rotationof shaft 3| through an angle proportional to the amount of unbalance.Rotation of shaft 3| moves the slider over the balancing resistance 28through the medium of suitable reduction gearing 32, if necessary.Automatic galvanometer mechanism of this general type is disclosed in U.S. patent to Ulrich, 1,647,383 granted November 1, 1927.

Rotation. of the shaft 3| to whatever angular extent is necessary torebalance the bridge moves the rotor of master motor 33 to acorresponding angle. This motor is provided with a stator winding 34supplied with alternating current from any suitable source. The rotorwinding is shown of well-known three-phase construction, three points ofwhich electrical degrees apart, are connected by the three wires 38, 39and 4D to a similar winding on each driven motor, of which there may beany suitable number depending upon the number of repeaters that are tobe controlled from the one pilot conductor 2! One such driven motor isshown as comprising a rotor 35 and a stator 36 included inside theshielded compartment ll, but in a compartment which is carefullyshielded from the repeater circuit. The

rotor 35 is connected to any suitable reduction gearing 3?. that may benecessary or desirable and through this gearing is connected to therotor of the variable condenser It as indicated.

If the temperature of the cable including line H3 changes, acorresponding temperature change occurs in pilot conductor 2| causingthe bridge 22 to become unbalanced. Let it be assumed that the change istoward a higher temperature of the cable requiring an increase in thegain of the repeater 8. When the bridge becomes unbalanced as assumed,the automatic galvanometer mechanism 29 rebalances the bridge byrotation of shaft 3! through a suitable angular distance =causin theslider to move along the resistance 28 until the:

bridge is balanced. This rotates the rotor :of the master motor 33which'is electrically interlocked, as described, to the motorsassociated with allof the repeaters, at the repeater station RR, to beregulated, causing the latter motors to rotate a corresponding amountand take up a corresponding position. This movement of rotor 35 producesmovement of the rotor of condenser H5 in such direction as to decreasethe amount of voltage that is fed back tO'the input of the amplifier 8.Since the voltage fed back is in a direction to reduce the gain of theamplifier 8, a decrease in the fed back voltage causes the resultantgain to be increased. The proportionality of the various parts is suchthat the increase in gain of repeater circuit 8 just compensates for theincrease in attenuation of the line l9 that is assumed to have takenplace. A decrease in temperature of the cable results in a movement ofthe motors in a reverse direction to decrease the gain of the repeaterby an appropriate amount.

A description will be given of the manner of functioning of theregulating apparatus associated with the long pilot wire PL i of Fig. land the cooperation between this regulating apparatus and that alreadydescribed which is controlled by the short pilot wire. For this purposeit will be assumed that the switches is of Fig. 2 are in the positionshown in the drawing, thus placing the regulating network I8 in shuntacross the line between the repeaters 8 and 29. Switch 2! is alsoassumed to be in the position shown in the draw ing so that the leads 42are included in series with the pilot conductor 2|.

The long pilot wire PL4 or 59 is shown leading to a bridge 5! which maybe similar to bridge 22 already described. Bridge 5! includes abalancing resistance 52 and has connected to its opposite diagonals thebattery 56 and an automatic galvanometer 53, respectively. Automaticgalvanometer 53 in operating to rebalance the bridge 5| when unbalanceoccurs, rotates shaft 54 causing the slider to move along the resistance52 by means of the mechanical connection between the slider and shaft 54through suitable gear box 55. Shaft 54 leads to the rotor of mastermotor 5'! which is connected to the rotor of the motors 59. Statorwindings 58 and 60 are indicated for the master motor and the drivenmotor. respectively, for supplying alternating current power thereto.Driven motor 59 is connected through suitable gearing 6!, if necessary,to shaft 62 which moves sliders over a number of resistances 63, 64 and65. Resistance 53 is connected to the leads 42 and is therefore insertedin series with pilot conductor 2 I. Each of the other resistances 64,65, etc. leads to a different network !8 associated with differentrepeaters, located at repeater station RR, to be regulated. The variableresistance 64 is for varying the shape of the characteristic of theequalizer l8 to which it is connected by leads 4|. With proper design ofnetwork l8 its shape is suitably varied by control of a singleresistance such as 64, as illustrated. Network 18 may be of the generaltype, disclosed in U. S. patent to Zobel 1,591,073 issued July 6, 1926or in U. S. pat- .ent :of Norton No. 2,019,624 issued May 19, 1936,Serial No. 726,471 filed May 19, 1934.

'Since'the variations in attenuation with change in temperature aregreatest at intermediate frequencies-of the band (e. g. 28 k. c.) it isnecessary t the shape of the equalizer l8 be such as to rofduce greatestchanges in network attenuaatthe two extreme ends of the transmitted d{2A succession of characteristic curves of rk, I8 taken at differentadjustments corresponding" to different temperatures will thereforeappear-asa succession of curves with greater separation at their extremehigh and low frequency regions than in the region of 28 kilocycles. Ifit were possible to design network [8 so that the loss at some onefrequency, (most desirable frequency being the one at which the flatregulator now operates) remained constant while the shape of itscharacteristic changed under control of resistance 64, it would not benecessary to interconnect the control mechanisms of the long pilot wireand the short pilot wire for mutual interaction. work is varied tocorrespond to a temperature change, the network has changed itscharacteristic at all frequencies in the utilized band as well as havingproduced the desired shape for connections. In other words, the totalattenuation change made by changing the amount of twist of network !8may be resolved into a flat variation (the same at all frequencies) plusa differential Variation which is least in the vicinity of 28 kilocyclesand increases for frequencies on either side of this minimum value. Thecomponent of this attenuation change which is the same at allfrequencies serves no useful purpose and is, in fact, undesired since itis the function of the shortpilot wire regulator mechanism to effect allor -rite fiat gain change that is necessary for complete "compensationof the cable.

In accordance with this invention the long Wire and the short wireregulating mechanisms are so interrelated that the flat gain changeintroduced by the short pilot wire regulator compensates for the fiatcomponent of the change in loss introduced by the network 18 so that theover-all flat gain change for the entire repeater is always kept at thecorrect value. This is accomplished specifically in the circuit asdisclosed by connection of variable resistance 63 in circuit with theshort pilot wire 2|. Whenever the regulating mechanism operates to varyresistance 64 to change the amount of the twist correction by thenetwork 18 resistance 63 is also varied to control bridge 22 and itsregulating mechanism to vary the condenser Hi to effect a flat gainchange in the repeater circuit 8 which exactly counteracts the efiect ofthe flat component of the gain change introduced by network l8.

The use of the electrically interlocked motors as described makes forgreat accuracy of control with s'implication of apparatus. In the usualrepeater station space is at a premium and it is a great advantage to beable to locate pieces of apparatus where the wiring or other structuralfeatures is kept as simple as possible. The motors themselves can bevery small since their load consists merely of the rotor of an aircondenser andeven this small load is reduced through gearing. Thethree-wire leads can be carried to any amplifier location withoutcomplication. Angular movement of the master controller shaft isrepeated with great precision. Applicant has found it practicable todrive fifty gain adjusting motors from a single master motor, and thisis not given as a limit but rather as one practical case.

The invention is not to be construed as limited to the details or thespecific arrangement or the actual numerical values that have been givenin connection with the illustrative embodiment, but it is to beunderstood that various modifications and departures from the specificdisclosure may be made within the spirit and scope of the appendedclaims.

What is claimed is:

I. In a regulating system for repeaters, a plurality of repeaters to besimultaneously regulated, a mechanism at each repeater regulatable by acontinuous movement throughout the extent of movement required to efiectregulation, a main control member movable to different extents by acontinuous movement, rotors connected individually to said mechanismsand to said control member, and an electrical interlock between saidrotors whereby movement of said control member causes like movement ofeach of said mechanisms.

2. In a transmission regulating system for a line having repeaters atintervals, means at each repeater point for changing the gain of therepeater for a wide range of frequencies in response to a change in linecharacteristic, means at certain repeater points to change the shape ofthe overall repeater characteristic to compensate for differences inchange in transmission characteristic at different portions of thefrequency range,

' one of said two means at said certain repeater points modifying theoperation of the other to more fully compensate for changes in linecharacteristic throughout the total frequency range.

3. In a transmission regulating system for a line having repeaters atintervals for transmitting waves of a band of frequencies, a short pilotcurrent circuit controlling the gain of a repeater, a long pilot currentcircuit controlling the shape of the overall characteristic of saidrepeater, and means controlled by the long pilot current circuit forvarying the control exercised by the short pilot current circuit.

4. In a transmission regulating mechanism for a plurality of repeatersat a repeater station common to a plurality of lines, one regulatingmechanism controlling the gain of all of the repeaters, anotherregulating mechanism controlling the shape of the characteristic of allof said repeaters, and means controlled by one of said mechanisms forvarying the control exercised by the other of said mechanisms to preventover or under regulation of said repeaters at any portion of thetransmitted range.

5. In a transmission regulating system, a plurality of repeaters to beregulated, a movable element associated with each repeater forcontrolling a characteristic of the repeater, a master regulator havinga movable regulating member connected to a master motor, a motorassociated with each repeater for driving said movable element to effectan adjustment of the repeaters, a Winding of each of said motors,including said master motor, having taps at electrically separatedpoints of the winding, the corresponding points of the windings of theseveral motors being interconnected whereby movement of the rotor of themaster motor causes equal movement of the rotor of each of the othermotors.

6. In a transmission regulating system, a plurality of repeaters, avariable air condenser associated with each repeater to control itsgain, a motor for each repeater for varying the adjustment of suchcondenser, a master control motor and a three-phase electricalinterlocking circuit extending between said master motor and all of theothers of said motors.

"I. In a transmission regulating system for a broad band transmissionsystem, the combination with a repeater of one pilot Wire regulatingmechanism for adjusting the gain of said repeater, another pilot wireregulating mechanism for adjusting the shape of the repeatercharacteristic and incidentally varying its characteristic over thetransmitted band, as a whole, and means operated by said other pilotwire regulating mechanism affecting the first-mentioned pilot wiremechanism to modify its gain adjustment to compensate the effect of thevariation by said other pilot wire regulating mechanism of thecharacteristic over the transmitted band as a whole.

FRED A. BROOKS.

